Air carrier Flight Attendant reported confusion regarding the transport of a Hover Board. The crew determined that Hover Boards are not allowed onboard.

Narrative

On Flight XXXX ZZZ - ZZZ1 passenger in [row] XX brought on a Hover Board. The gate agent verify with the Manager whether the Hover Board could be stowed in the plane? She said they said 'yes'. Even though she knew that wasn't correct. Flight Attendant 4 (FA) came to the back and told me they allowed a Hover Board on board and she didn't think it was allowed. So we looked it up and under Carry On Baggage; Manual; it states Hover Boards (do not accept) X- Carry- On or X- Checked. So I went to the front and told [the purser]. Asked where did I find it and questioned weather my IPAD was updated. Then I looked at the Captain (CA) and told him if they don't remove the Hover Board I'm not flying. So CA got up and he asked gate agent to get passenger. I showed [the purser] how to find the Hover Board under carry-on; on her personal iPad. CA & First Officer (FO) show passenger the iPad that Hover Boards were excluded from flying on the aircraft. CA told me to get the Hover Board. The husband brought Hover Board forward. The passenger; stated to me that they had called our customer service before they brought the Hover Board on vacation and they stated it was OK; plus the Hover Board had flown on [another airline] already from ZZZ1 - ZZZ. I told her that the previous crew had missed it and it was in our manual stating that it could not fly and I didn't feel safe with the Hover board on board our aircraft; especially since it was written in our guide lines. I know I should not write my opinion; but [the purser] did not think that Carry-On was part of our manual; because the information was not located in the manual. The second guessing between us was probably the most difficult confronting the passenger. Another suggestion is if we can get an explanation to why it can not be on the plane?; what can happen?; what can we explain to the passengers.